An unmanned Russian cargo ship has docked successfully at the International Space Station, where it was anxiously awaited by the U.S.-Russian crew after the successive failures of two previous supply missions.

The Progress M-28M ship, which is carrying 2.5 metric tons of fuel, oxygen, water, food and other supplies, was launched into orbit on Friday from the Baikonur launch pad in Kazakhstan. Russian Mission Control said it docked successfully Sunday in the automated mode at the orbiting space station.

It may not be space debris, errant asteroids, supply shortages, thruster malfunctions or even the malevolent aliens envisioned in so many Hollywood films that thwart astronauts on any mission to Mars. It may be the ubiquitous galactic cosmic rays.

Researchers said on Friday long-term exposure to these rays that permeate space may cause dementia-like cognitive impairments in astronauts during any future round-trip Mars journey, expected to take at least 2-1/2 years.